1. Field of the Invention
The present invention relates to a gas turbine engine intended for use as an aircraft engine, of the type comprising a gas generator which supplies two interdigitated, contra-rotating, low-speed, power turbines.
2. Summary of the Prior Art
FR-A-2 535 394 describes a gas turbine engine of this type in which the power turbines are arranged downstream of the gas generator and are directly driven by the hot gases emerging from the generator. The turbines, directly and without any reduction gearing, drive either two contra-rotating propeller stages, or two ducted fan stages to provide propulsion. Two mounting solutions are proposed. One envisages arranging the propellers or the fans at the rear of the engine, which presents problems and difficulties when the engine is to be mounted under the wing of an aircraft. The other envisages mounting them at the front of the engine, which requires the use of connecting shafts in order to effect the drive, the location of such shafts also presenting problems.
FR-A-2 560 642 describes a gas turbine engine of the same type in which a contra-rotating supercharging compressor is associated with the contra-rotating forward mounted fans. Means for regulating the pitch of the blades of a fan stage is incorporated and permits flow reversal to be obtained.
FR-A-2 606 081 describes a gas turbine engine of the above-mentioned type in which, in relation to the direction of travel of an aircraft propelled by the engine, the gas flow through the gas generator is forward from an annular chamber arranged at the rear of the engine and is supplied with air by an air intake assembly comprising a plurality of ducts disposed around the outer casing of the engine, and the hot gas flow emerging from the gas generator is reversed so as to flow in a rearward direction through the power turbines, the internal arrangement of the engine comprising, in succession from front to rear:
the interdigitated contra-rotating power turbines and the axial outlet duct from the gas generator in partial radial superposition; PA0 the turbine stages of the gas generator; PA0 the combustion chamber; PA0 the compression stages of the gas generator; and, PA0 the annular air inlet chamber of the gas generator. PA0 said front fan; PA0 said rear fan and, in radially superposed relation, part of said air intake means; PA0 said interdigitated power turbines and, in radially superposed relation, said axial duct from said gas generator; PA0 said gas generator turbine stages; PA0 said combustion chamber; PA0 said gas generator compressor stages; and PA0 said annular chamber of said air intake means.
According to this document the contra-rotating power turbines are arranged to drive two contra-rotating propeller stages situated at the same longitudinal level as the power turbines, the engine thus constituting a forward propeller turboprop unit of the type known as a "tractor propfan".